1. Field of the Invention
The present invention relates to a photopolymerizable composition and more particularly to a photopolymerizable composition comprising an addition polymerizable compound having ethylenically unsaturated bonds, a photopolymerization initiator and optionally a binder, which is useful as a light-sensitive layer of presensitized plate for use in making lithographic printing plates, a light-sensitive layer for use in making color proofs, a photoresist for use in making print circuit board and the like.
2. Description of the Prior Art
It has been well known to form duplicates of images according to a photographic manner utilizing a light-sensitive composition composed of a polymerizable compound having ethylenically unsaturated bonds and a photopolymerization initiator, which optionally contains a proper binder capable of forming a film and a heat polymerization inhibitor. As disclosed in U.S. Pat. Nos. 2,927,022; 2,902,356 and 3,870,524, such kind of light-sensitive compositions make it possible to provide desired images of hardened light-sensitive composition by forming a proper film therefrom, exposing it to light through a negative carrying desired images thereon and removing unexposed areas by selectively dissolving them with a proper solvent (hereunder referred to as simply development), since the light-sensitive composition causes photopolymerization by irradiating it with light and thus causes hardening to make the exposed portions insoluble in a developer. It is a matter of course that this kind of light-sensitive composition is very useful for forming a presensitized plate (hereunder referred to as PS plate), a photoresist or the like.
Moreover, it has been proposed to incorporate, into the foregoing light-sensitive composition, a photopolymerization initiator for the purpose of improving the light-sensitivity thereof since a sufficient light-sensitivity cannot be expected by simply using a polymerizable compound having ethylenically unsaturated bonds and there has been used such a photopolymerization initiator as benzil, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone or 2-ethylanthraquinone.
However, when such a photopolymerization initiator is used, the resultant light-sensitive composition is inferior in sensitivity to hardening and thus it takes a long period of time to expose it to light to form images. For this reason, the image having a good performance is not reproduced in the case of the reproduction of fine images even when there is a slight vibration in the operations of imagewise exposure. In this case, it is further required to increase the dosage of radiant rays from a light source for exposure and, therefore, it must be provided for a means for diffusing a great deal of heat generated during the exposure operation. In addition, the heat generated exerts a severe influence on the film of the light-sensitive composition and thus causes the deformation and the change of properties thereof.
Recently, it has been investigated to improve the light-sensitive composition in its sensitivity to ultraviolet light and since UV projection techniques have already been put into practical use for manufacturing PS plates or the like the corresponding light-sensitive materials of high sensitivity is now under development. However, such light-sensitive materials are still insufficient in sensitivity.